Human Body (DK Eyewitness Books)
Human Body creatures on
Earth. This intelligence, linked with natural curiosity, gives us a unique opportunity to understand our own bodies. Knowledge gained over centuries tells us that while we may look different from the outside, our bodies are all constructed in the same way. The study of anatomy, which explores body structure, shows that internally we are virtually identical—aside from differences between males and females. The study of physiology, which deals with how the body works, reveals how body systems combine to keep our cells, and us, alive. Human beings are all related. We belong to the species Homo sapiens, and are descendants of the first modern humans, who lived in Africa 160,000 years ago and later migrated across the globe.
It takes around 100 trillion cells to build a human body. There are 200 different types of these microscopic living units, each of which is highly complex. Similar cells join together to make a tissue, two or more tissues form an organ, and linked organs create a system. Body systems interact to form a living human being. To understand how this arrangement works, see the digestive system (right).
Myths, magic, and medicine made sculptures and cave paintings of figures with recognizable human body shapes. As civilizations developed, people started to think about the world around them and study their own bodies more closely. The ancient Egyptians, for example, mummified millions of bodies, but little of their anatomical knowledge has survived. Until the time of the ancient Greeks, medicine—or the care and treatment of the sick and injured—remained tied up with myths, magic, and superstition, and a belief that gods or demons sent illnesses. The “father of medicine,” Greek physician Hippocrates (c. 460–377 ) taught that diseases were not sent by the gods, but were medical conditions that could be identified and treated. During the Roman Empire, Galen (129–c. 216 ) established theories about anatomy and physiology that would last for centuries. As Roman influence declined, medical knowledge spread east to Persia, where the teachings of Hippocrates and Galen were developed by physicians such as Avicenna (980–1037 ).
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